Can I get overdrive?
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Senior User
Joined: Jul 2003
Posts: 165
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From: St. Louis, MO
Can I get overdrive?
Yes, it's one of those questions asked over and over again. What options do I have for my 351M? I have a C6 with 2.75 gearing outback and would like to have an overdrive unit or at least a 4 speed for descent highway mileage.
Posting Guru
Joined: Dec 1999
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From: Benton County, MN
IMHO, you need to look real hard at your set up. Your signature says you have a 79 F-150 super cab. Is this the truck in Question? Is it 4WD or 2WD. Either way having 2.75 gears and an overdrive in that truck may not be a very good combination. You may bog too much when actually trying to use overdrive. If its 4WD the chances of this being true increases with larger tires. Having a 351M doesn't help very much either since these engines are pigs. If your willing to spend a lot of money on overdrive to save a few bucks in gas, it may be better to invest in a car and use the truck when you need it. Just my opinion.
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Senior User
Joined: Jul 2003
Posts: 165
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From: St. Louis, MO
Well, yes 2.75 gearing is good for highway speeds and I'm not really getting poor gas mileage but I was just wondering if there were any other options to improve my mpg. True be told, I'd rather have 3.20 or 3.55's and 4 speeds, but that won't happen anytime soon.
Thanks for all the input guys. Oh, I'm running stock 235/75 15's - just so you know.
Thanks for all the input guys. Oh, I'm running stock 235/75 15's - just so you know.
Postmaster
Joined: Dec 2002
Posts: 3,959
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From: USA
You would most likely improve your mileage around town, towing, and driving uphill by swapping to a lower ratio gear (numerically higher). Since you have a 351M, I assume your truck is from the '70's and probably weighs a fair amount. With lower gears, your engine doesn't have to work so hard getting the truck moving so it uses less fuel when accelerating or climbing a grade.
I found that to be true when I went from 3.55's to 4.56's in my 6500 + lb one ton with 33" tires and an underpowered 351. My mileage under most driving conditions went up, except for cruising fast on the freeway, and that is mostly because with my C6 transmission, I have no OD.
I would think that 3.55 gears would give you better mileage under most conditions and more power than you have now.
I found that to be true when I went from 3.55's to 4.56's in my 6500 + lb one ton with 33" tires and an underpowered 351. My mileage under most driving conditions went up, except for cruising fast on the freeway, and that is mostly because with my C6 transmission, I have no OD.
I would think that 3.55 gears would give you better mileage under most conditions and more power than you have now.
Last edited by SoCalDesertRider; Apr 3, 2004 at 06:19 PM.
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From: Saint Charles, MO USA an
Switch out the carb. A decent 4 barrel should give you the power you need and some gas conservation. The only thing new gears will do is reduce your top end speed and if you drive highways it sucks.
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